Protein For Growth
Ok, so I am sure that you are aware of the importance of protein for muscle growth and repair. Protein supplies the essential building blocks (amino acids) that fuels what we call protein synthesis. It is this protein synthesis which allows you to build new muscle over time and, hold onto your existing muscle. But, one of the burning questions that people still ask today is: just how much protein is needed to maximise muscular hypertrophy gains? Well, recent studies might point to an answer.
Resistance Training And Muscular Hypertrophy
The first thing you need to know is that resistance training is by far the most effective manner to increase your muscular hypertrophy gains. There is just no question about this! If your goal is to put on lean muscle, build up strength, improve body composition, heck, even lose fat! Then implementing a regular resistance training plan is by far the most effective way to do this. Let me put it this way, you can consume all the protein in the world, but if you don’t participate in any decent resistance training program, then your muscular hypertrophy gains are going to be almost non-existent. However, you can maximise the gains you do achieve through your resistance training, by ensuring that your daily protein intake is optimal. Although there is no one size fits all recommendation for daily protein intakes, recent studies have helped clarify potential ranges to aim for if looking to maximise gains in response to resistance training.
The Optimal Protein Intake Range?
In attempting to find out what the optimal protein intake would be in order to maximise resistance training induced muscular hypertrophy gains, Morton et al. (2018) conducted a meta-analysis from 49 studies and 1863 adult healthy participants. On pooling of this data, Morton et al. found that dietary protein supplementation up to approx. 1.62g/kg/day in response to prolonged resistance training (6 or more weeks training), resulted in significant increases in 1 RM strength (average: 9% or 2.49kg), fat free mass (average: 27% or 0.30kg) and, muscle fiber cross-sectional area (average: 310um2 or 38%). On closer inspection of the data, it was further found that protein supplementation on fat free mass gains was more effective in those that were resistance-trained. Likewise, the efficacy of protein supplementation on resistance-training induced gains became less effective with increasing age.
Morton et al. (2018). Forest plot figure shows that on average, protein supplementation leads to a significant increase in 1RM maximum strength in both trained and untrained healthy adults.
Morton et al. (2018). Forest plot figure shows that on average, protein supplementation leads to significant increases in fat free mass in both untrained and trained healthy adults. Furthermore, the consistent impact on fat free mass gains in trained adults supports the notion that trained indviduals require higher levels of protein suppementation in order to stimulate muscle gains.
So, what can explain these results? Well, it all goes back to protein balance. That is, there is a constant flux between muscle protein synthesis and muscle protein breakdown within the muscle. When muscle protein synthesis is greater, new muscle proteins can be produced and their accrual over time leads to the synthesis of new lean muscle tissue (anabolism). But, when muscle protein breakdown is greater, muscle proteins become degraded and muscle tissue can be broken down (catabolism). In response to resistance training, there is both a rise in muscle protein synthesis and breakdown. In order to make sure hypertrophy is optimised, muscle protein synthesis needs to be maximised to allow for maximal accumulation of new muscle proteins over time (Damas et al 2016).
Also, studies have shown that the muscle protein synthesis responses following resistance training can be increased in a dose-dependent fashion following protein supplementation (Yang et al. 2012; Moore et al. 2008). However, given that Damas et al. (2016) only found correlations between muscle protein synthesis responses and muscular hypertrophy in the later weeks of resistance training, it is likely that hypertrophy is only set in motion through the accumulated, intermittent increases in muscle protein synthesis following resistance training. In line with this, protein supplementation would likely maximise these post-exercise muscle protein synthesis rises thus ensuring maximal production of those essential muscle building proteins.
Damas et al. (2016). Figure shows the increase in fiber cross-sectional area following first week (T1), third week (T2) and tenth week (T3) of resistance training. In the tenth week (T3), fiber cross-sectional area increases significantly from baseline.
Damas et al. (2016). The increase in muscle protein synthesis (FSR) in T2 and T3 was correlated with increases in fiber-cross sectional area, but not at T1. It is likely that hypertrophy occurs due to an accumulation of intermittent increases in muscle protein synthesis over time. It seems the acute increases in muscle protein synthesis act to initiate some downstream pathways which initiate hypertrophy over the long-term.
Indeed, Morton et al. (2018) found a dose-dependent increase in fat free mass with increases in protein supplementation up to approx. 1.62g/kg/day in healthy adults. Above this threshold point, there were no further increases in fat free mass. Just like the dose-response relationships observed by Yang et al. (2012) and Moore et al (2008), it is likely that at a protein supplementation level of 1.62g/kg/day, muscle protein synthesis responses were maximised, leading to maximal levels of protein creation over the course of the resistance training period, hence the gains observed in fat free mass.
Morton et al. (2018). Figure shows the dose-dependent relationship between increases in fat free mass and total protein intake. The optimal range for healthy adults seems to be approx. 1.6g/kg/day. However, this is not a one size fits all. Some individuals might need even more depending on training experience and some, less. Ideally, a range of 1.6-2.2 should be considered, with individuals adopting the top end of this range in order to maximise muscular hypertrophy gains.
An interesting observation by Morton et al. (2018) was that protein supplementation was more effective in resistance-trained adults. But why? Well, as suggested by Kim et al. (2005), resistance training might have a sort of dampening effect on subsequent rises in post-exercise muscle protein synthesis. SInce resistance training for the very first time is likely to cause large disturbances in muscle homeostasis, the outcome will probably lead to a production surge in a wide range of proteins to correct this. After a while, these large disturbances will gradually reduce and the muscle protein response undergoes what KIm et al. suggest as ´refinement´. In other words, the type and magnitude of the proteins that are produced changes, leading to a smaller post-exercise muscle protein signal in those more advanced. This refinement process is likely to be initiated through changes in the sensitivity of various downstream protein signalling pathways. Due to this, Morton et al. suggest that advanced lifters likely need more protein than those less trained in order to stimulate the muscle protein synthesis responses needed for more gains.
Kim et al. (2005). Figure shows the changes in acute mixed protein (A) and myofibrillar protein rates (B) following training of a resistance trained leg and untrained leg. There is a significant increase in mixed protein synthesis following training of the untrained leg, but not following training of the trained leg. Moreover, myofibrillar protein synthesis remains unchanged between training of the trained and untrained legs. It is likely that resistance training for the first time, causes a significant disruption in muscle homeostasis which initiates a surge in a range of proteins (accounting for the increase in mixed protein synthesis). However, given that myofibrillar rates remained unchanged but do increase in response to training, it is likely that the post-exercise protein synthesis signal becomes refined. Switching from mixed to primarily myofibrillar protein production. This might be due to changes in downstream signalling pathways.
The effect of protein supplementation on fat free mass may be decreasing with age. Previous research has found that older adults need higher doses of protein [Yang et al. 2012 (approx. 40g)] in comparison to younger adults [Moore et al. 2008 (approx. 20g]) in order to maximise muscle protein synthesis responses following exercise. It was suggested that older adults might have a blunted anabolic response to exercise and in fact, the threshold to anabolic stimuli might be higher in older adults. Therefore, it seems plausible that to stimulate a rise in muscle protein synthesis comparable with that of younger adults, a higher dose of protein would be needed (Yang et al, 2012). It has to be mentioned that in the meta-analysis performed by Morton et al, older respondents were only given supplemental daily protein doses of approx. 20g/day. It is therefore likely that increases in fat free mass would have been seen if the 40g/day amount had been reached.
Yang et al. (2012). Figure shows the changes in muscle protein synthesis (FSR) in response to increases in ingested whey protein in 37 elderly men (approx. 71 years of age). The black bars represent the changes in protein synthesis following resistance training. Ingestion of 40g of whey protein produced the greatest increase in post-exercise protein synthesis.
Moore et al. (2008). Figure shows the changes in muscle protein synthesis (FSR) following resistance training in six healthy young males (approx. 22 years of age) with increasing doses of protein. Here, a dose of 20g of protein was found to produce the greatest increases in post-exercise muscle protein synthesis, with no significant increases beyond this.
Well firstly, protein is important for general growth and repair of tissues. Moreover, resistance training is the best stimulus you can use for muscular hypertrophy gains. But, if you want to maximise the positive effects of resistance training, then getting in enough daily protein is essential. The question is: how much daily protein do you actually need? Well, it seems that on average for healthy adults, 1.6g/kg/day seems like the sweet spot to aim for. Some may need more, some less, but it gives us a target to aim for. Especially if you want to maximise your muscular hypertrophy gains. Please don’t take 1.6g/kg/day as a one size fits all figure! Whether you consume protein from supplements or from food, it does not matter (but real food would be better!), as long as you are reaching your daily targets. There are many debates about the influence of protein timing, how much protein per meal and the protein source on fat free mass gains. The general consensus is that these things have very little if any effect, and that your major focus should be on total DAILY protein intake. If you can achieve this target, then you are well on your way to maximising your hypertrophy gains in response to the work you do in the gym.